As a measurement method of elongations of a specimen, there are heretofore known, for example, a direct measurement method in which a testing person reads directly elongations of a specimen by applying a scale to it; a non-contact measurement method for which visible rays are used; a contact measurement method in which a specimen is attached with a jig for elongation measurement to determine the elongations from displacement magnitudes of the jig; etc.
The direct measurement method, however, is not suited for high accuracy measurement since the length between the bench marks moving every moment is pursued with the unaided eyes. The non-contact method with the aid of visible rays, when applied to a wide variety of colored specimens having a large elongation such as plastics or rubbers, has encountered a problem in which the texture of a specimen is discolored as the elongation of it increases and the contrast between the texture and the bench marks is changed. Accordingly, the method is defective in that elongations of all the specimens cannot always be measured accurately. For instance, the case of a black specimen will be referred to. When the black specimen is marked with white bench marks thereon and drawn, the black specimen is discolored to such a white hue that cannot be disinguished from the white color of the bench marks. When the black specimen is marked with bench marks of a red series color and drawn, before drawing the red color of the bench marks is brighter than the black color of the specimen, but as the specimen is drawn under load, it becomes discolored to a white hue brigher than the red series color of the bench marks and the brightness of the specimen is thus inverted. As a consequence, the detection of the bench marks is not feasible. Further, visible rays from the projector are reflected by the discolored white hue portion of the specimen and are incident upon the optic, so that the detection of the bench marks is more impossible. For the reasons above, it is impossible to use visible rays of the measurement of elongations of a wide variety of specimens and all colored specimens.
The contact measurement method is disadvantageous in that it is troublesome to mount the jig for elongation measurement on the specimen whenever it is measured, and in that the weight of the jig may often be responsible for causing errors. In particular, in the case of a specimen such as a film which is susceptible to break-down even under a slight tensile load, a further drawback is seen in the fact that a load is imposed on the portion of the specimen to which the jig is attached, from where the specimen is broken down, so that it is not possible to measure elongations.
Any of the prior art measurement methods have thus many problems and drawbacks to be solved and improved for the measurement of elongations with high accuracy and precision.
With a view to coping with the prior art situation as described above, this invention is designed for measuring elongations of a wide variety of colored specimens which it has been heretofore difficult to measure by any method regardless of the non-contact method and the contact method, with high accuracy.
Therefore, an essential object of this invention is to provide a tensile tester intended for a non-contact method having an improved measurement apparatus by adopting an ultraviolet lamp as a light source of a projector.